The present invention relates to solid-state imaging apparatus such as digital camera for outputting video signals, and more particularly relates to a solid-state imaging apparatus in which vertical stripe-like noise and horizontal shading can be corrected.
Such solid-state imaging devices as CCD image sensor or MOS image sensor are among the apparatus for converting light into electric signals and are widely used for example in digital camera. FIG. 1 is a circuit diagram showing an example of construction of a prior-art MOS image sensor. The MOS image sensor according to this example includes: unit pixels 2011 each having a photodiode PD1 serving as photoelectric conversion section, an amplification transistor M1 for amplifying detection signal of the photodiode PD1, a reset transistor M2 for resetting detection signal of the photodiode PD1, a row select transistor M3 for selecting each row of a pixel section, and a pixel power supply VDD; a vertical scanning section 2012 for driving the unit pixels 2011; a column select line 2013 connected in common to the unit pixels 2011 arranged in a column direction, for outputting signal from the unit pixels 2011; a biasing transistor M5 for flowing a constant current to the column signal line 2013; a bias current regulating voltage line VBIAS for determining a current value of the biasing transistor M5; a clamping capacitor C11 connected to the column signal line 2013; a hold capacitor C12 for retaining change in voltage of the column signal line 2013; a sample-and-hold transistor M12 for connecting between the clamping capacitor C11 and hold capacitor C12; a clamping transistor M11 for clamping the clamping capacitor C11 and hold capacitor C12 to a predetermined voltage; a column select transistor M13 connected at one terminal thereof to the hold capacitor C12, for reading signal from the hold capacitor C12 of each column; a horizontal signal line 2015 to which the other terminal of the column select transistor M13 is connected; an output amplifier 2016; and a horizontal scanning section 2014 for driving the column select transistor M13. It should be noted that the clamping capacitor C11, hold capacitor C12, clamping transistor M11, and sample-and-hold transistor M12 together constitute a noise suppressing section 2017.
In thus constructed image sensor, it is possible to suppress variance in the amplification transistor M1 of unit pixel by means of the noise suppressing section 2017 provided for each column where correlation double sampling is effected. If variance exists in the noise suppressing section 2017 itself, however, a problem occurs that such variance causes an overlapping of vertical stripe-like noise or horizontal shading on obtained pixel signals.
A method as will be described in the following has conventionally been used to correct such vertical stripe-like noise or horizontal shading. FIGS. 2 and 3 are an illustration for schematically showing construction of an image sensor capable of correcting vertical stripe-like noise and horizontal shading as disclosed for example in Japanese Patent Application Laid-Open 2000-261730, and a block diagram showing construction of solid-state imaging apparatus mounting the image sensor.
FIG. 2 shows construction of the MOS image sensor shown in FIG. 1 in a simplified manner, where like components as in the image sensor shown in FIG. 1 are denoted by like reference numerals. Provided within an entire pixel region 2001a of pixel section consisting of a plurality of unit pixels arranged in a matrix are an OB region 2001c the surface of which is covered with a light-shield film, and an effective pixel region 2001b to be used in actual image taking. An upper side of OB region 2001c is referred to as a vertical OB region 2001d. 
The solid-state imaging apparatus shown in FIG. 3 includes: an image sensor 3010; A/D conversion section 3020 for converting signal from the image sensor 3010 into digital signal; a vertical OB region addition averaging section 3030 for extracting signals corresponding to the vertical OB region 2001d of image sensor 3010 from the digital signals outputted from A/D conversion section 3020 to obtain their average by addition in column direction; a line memory 3040 for retaining signals from the vertical OB region addition averaging section 3030; a subtracting section 3050 for subtracting the signals (correction data) retained at the line memory 3040 from imaging signals outputted from A/D conversion section 3020; and an image processing section 3060 for effecting image processing of the signals from the subtracting section 3050 so as to output image signal.
When imaging signals are acquired in thus constructed solid-state imaging apparatus, what is obtained by the averaging by addition in column direction of the signals in the vertical OB region 2001d is retained at the line memory 3040 as data for correcting vertical stripe-like noise and horizontal shading. At the time of normal image taking, then, the vertical stripe-like noise and horizontal shading are corrected by subtracting the correction data retained at the line memory 3040 from imaging signals. Here the reason for effecting an addition averaging along the column direction is to make it less susceptible to random noise components.
Further, Japanese Patent Application Laid-Open Hei-10-313428 discloses the following technique. In particular, after attaining a condition where light does not enter the image sensor, correction data by an addition averaging in column direction are obtained from outputs in such condition. The vertical stripe-like noise and horizontal shading are thereby corrected.